Semiconductor pressure sensor and pressure sensing device

ABSTRACT

The object of the present invention is to propose an etch channel sealing structure characterized by excellent impermeability to moisture and resistance to temporal change of the diaphragm in the pressure sensor produced according to the sacrificial layer etching technique, and to provide a pressure sensor characterized by excellent productivity and durability. After a very small gap is formed by the sacrificial layer etching technique, silicon oxide film is deposited by the CVD technique or the like, thereby sealing the etch channel. Further, impermeable thin film of polysilicon or the like is formed to cover the oxide film. 
     This allows an etch channel sealing structure to be simplified in the pressure sensor produced according to the sacrificial layer etching technique, and prevents entry of moisture into the cavity, thereby improving moisture resistance. Moreover, sealing material with small film stress reduces temporal deformation of the diaphragm.

TECHNICAL FIELD

The present invention relates to a semiconductor sensor having amicro-cavity structure and an actuator created based on the sacrificiallayer etching technique, and particularly to an electrostaticcapacitance semiconductor pressure sensor.

BACKGROUND TECHNIQUE

The prior art related to the present invention is disclosed in JapaneseApplication Patent Announcement Publication No. Hei 08-501156 as shownin FIG. 23, for example. This Patent describes the pressure sensormanufactured according to the sacrificial layer etching technique.Sacrificial layer etching is formed in the following process, forexample: A sacrificial layer to be removed later is formed on thesubstrate in advance, and part of this layer is removed. A filmremaining as a structure or anchor is formed thereon, and the endportion of the sacrificial layer is exposed to the outside. This portionis removed by etching, then a sensor and actuator are manufactured withthe structural film. Or this process is repeated several times to form amore complicate structure. A fixed electrode 3 is formed on the surfaceof a silicon substrate 1 and a polysilicon diaphragm 6 is formedthereon, with a gap 7 located in-between. This gap 7 is formed byetching and removing the sacrificial layer already formed in this areathrough an etch channel 12 provided on part of polysilicon diaphragm 6.To close this etch channel 12 and to provide vacuum sealing of the gap7, silicon oxide film 8 is formed to cover the whole surface of thepolysilicon diaphragm 6 and part of the silicon substrate 1 are covered.As a result, gap 7 is formed as a vacuum sealed pressure referencechamber, and a capacitor is formed between the fixed electrode 3provided on the substrate in the pressure reference chamber and aconductive diaphragm (movable electrode) consisting of the polysiliconfilm 6. If there is a change in the external pressure, polysilicon filmis displaced by differential pressure from the pressure referencechamber and a gap is changed between the two electrodes to cause achange in the capacitance of the capacitor. This change in capacitanceis used to detect the pressure.

Another prior art related to the present invention is disclosed in theJapanese Application Patent Laid-Open Publication No. Hei 11-14482. ThisPatent also refers to the capacitance pressure sensor manufacturedaccording to the sacrificial layer etching technique. In this case, asilicon nitride film is used to seal the etch channel.

To ensure reliability in the long-term use of the pressure sensor of theabove-mentioned structure, it is necessary to reinforce the hermeticstructure of the pressure reference chamber and to prevent temporalchange of the output. This requires careful selection of an adequatesealing structure of the etch channel and a proper sealing material.Japanese Application Patent Announcement Publication No. Hei 08-501156discloses a silicon oxide film used as a sealing material. However,silicon oxide film is permeable to moisture to some extent. In a highlyhumid environment, therefore, moisture may enter the gap through oxidefilm, causing changes in characteristics.

If the etch channel is sealed by nitride silicon film as disclosed inJapanese Application Patent Laid-Open Publication No. Hei 11-14482,characteristics of such a structure as diaphragm will be changed withtime since silicon nitride film has a very great film stress after filmformation. Accordingly, prevention of deformation requires reduction inthe thickness of silicon nitride film used for sealing. This will resultin restrictions on the size of the etch channel, etching failure of thesacrificial layer or increased etching time.

DISCLOSURE OF INVENTION

The present invention is intended to solve above-mentioned problems. Itsobject is to propose an etch channel sealing structure highly resistantto moisture and temporal change of the diaphragm in the pressure sensorproduced according to the sacrificial layer etching technique, and toprovide a pressure sensor characterized by excellent productivity anddurability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view representing a first embodiment of thepresent invention;

FIG. 2 is a plan view representing a first embodiment of the presentinvention;

FIG. 3 is a drawing representing how moisture passes through siliconoxide film;

FIG. 4 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 5 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 6 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 7 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 8 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 9 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 10 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 11 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 12 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 13 is a drawing representing part of the production process in thefirst embodiment of the present invention;

FIG. 14 is a cross sectional view representing a second embodiment ofthe present invention;

FIG. 15 is a drawing representing changes in the form of polysiliconfilm for surface protection in the second embodiment;

FIG. 16 is a plan view representing a third embodiment of the presentinvention;

FIG. 17 is a cross sectional view representing a reference capacitor inthe third embodiment;

FIG. 18 is a circuit diagram representing a capacity detecting circuitin the third embodiment;

FIG. 19 is a drawing representing the car engine control system using asemiconductor pressure sensor according to the present invention;

FIG. 20 is a cross sectional view representing a fourth embodiment ofthe present invention;

FIG. 21 is a plan view representing a fourth embodiment of the presentinvention;

FIG. 22 is a plan view representing a fifth embodiment of the presentinvention;

FIG. 23 is a cross sectional view representing the pressure sensoraccording to the prior art;

FIG. 24 illustrates a pressure detector according to the presentinvention; and

FIG. 25 illustrates a pressure detector according to the presentinvention.

BEST FORM OF EMBODIMENT OF THE INVENTION

The following provides a detailed description of the present inventionwith reference to the embodiments given in the drawings: FIG. 1 is across sectional view representing an embodiment of a semiconductorpressure sensor according to the present invention, and FIG. 2 is a planview thereof. The following describes the structure with reference toFIGS. 1 and 2. Monocrystal silicon substrate 1 is used for thesubstrate, and silicon oxide film 2 is formed on the surface thereof asan insulation layer. A fixed electrode 3 is formed on the silicon oxidefilm 2, and is made of polysilicon with phosphorus or other impuritiesdispersed thereon. Silicon oxide film 4 is formed on fixed electrode 3,and silicon nitride film 5 is formed on the surface thereof in order toprotect the substrate surface in the sacrificial layer etching processto be discussed later and to avoid leak current on the substratesurface. Polysilicon diaphragm 6 with part of its periphery fixed on thesilicon nitride film 5 is formed on the top of the silicon nitride film5, and a very small space 7 surrounded by the diaphragm and substrate isformed. The diaphragm substrate fixed portion 8 is annular but isfragmented at an equally spaced interval. The fragmented portion servesas an etch channel 12 leading to the gap. The etch channel is a servesas a path for etchant to enter the gap at the time of etching of thesacrificial layer to be discussed later. In order to close this etchchannel 12 and to vacuum-seal the gap, the substrate portion close tothe circumference of polysilicon diaphragm 6 and the surface of theouter wall of the polysilicon diaphragm 6 are covered with silicon oxidefilm 9 used for sealing. This sealing material is required to meet thefollowing conditions: Since it must cover the substrate and movableelectrode at the same time, it must be insulated to prevent leak currentflowing between them. Secondly, since it covers the side wall of thediaphragm, it must provide an excellent step coverage and sealingmaterial must not enter the inside of the gap. Thirdly, it must be ofcompact film in order to maintain hermeticity for a long time. Lastly,film can be formed in a short time. As a material meeting almost all ofthese conditions, silicon oxide film 9 formed by the CVD (chemical vapordeposition) method is adopted in the present embodiment. As shown inFIG. 3, however, the defect of sealing by silicon oxide film 9 is that,when exposed to the environment of high temperature and high humidityfor a long time, moisture may enter the gap through silicon oxide filmand may change the output characteristics. To eliminate this possibilityin the present embodiment, an impermeable polysilicon film 10 having adiffusion coefficient of water of 1×10⁻⁶ (m²/s) or less is formed on thesurface of the silicon oxide film 9, thereby preventing moisture frompermeating the silicon oxide film 9. This polysilicon film 10 is fixedto the ground potential made conductive by diffusion of phosphorus andother impurities, and serves as a shield against electrostatic dischargeto prevent ion particle and other external electrical charge fromaffecting the measurement of capacity.

The following describes the principle of operations with reference toFIG. 1: The silicon diaphragm 6 serves as a movable electrode, and formsa capacitor between it and fixed electrode 3, with a very small gaplocated in-between. The interior of the gap is a vacuum pressurereference chamber, and the silicon diaphragm 6 is deflected due todifferential pressure between the pressure reference chamber and theoutside. The electrode gap of the capacitor is changed by the deflectionof the silicon diaphragm 6 in response to the external pressure, and thecapacitance of the capacitor is subjected to changes. This change incapacitance is detected as a change in voltage by the switched capacitorcircuit, diode bridge circuit or the like.

The following describes the production method: The production processfor this sensor is based on LSI production process. Firstly, as shown inFIG. 4, the monocrystal silicon substrate 1 is subjected to thermaloxidation, and a silicon oxide film 2 serving as an insulating layer isformed on the top surface of the substrate. Then polysilicon film isformed on the surface thereof by CVD method and phosphorus and otherimpurities are dispersed to make it electrically conductive. Then adesired form of fixed electrode 3 is obtained by the photo etchingtechnique. Then as shown in FIG. 5, silicon oxide film 4 and siliconnitride film 5 are formed as barrier layers on the surface of thesubstrate according to the CVD method. After that, a sacrificial layer13 consisting of phosphate glass (PSG) is formed according to the CVDmethod, as shown in FIG. 6. The thickness of this sacrificial layer isequal to the height of a desired gap (electrode gap) to be formed later.This sacrificial layer 13 is processed by photo etching technique anddesired forms of the gap 7, diaphragm substrate fixed portion 8 and etchchannel 12 are obtained in one operation. As shown in FIG. 7,polysilicon film 14 is formed by the CVD method to the sacrificial layer13, and is made electrically conductive with phosphorus or otherimpurities dispersed thereon. Then it is processed by photo etchingtechnique to get a desired form of diaphragm 6, as shown in FIG. 8. Herepart of the sacrificial layer 13 is exposed to the outside from the etchchannel.

When this substrate is immersed in HF based etchant, only thesacrificial layer 13 is removed through the etch channel 12 as shown inFIG. 9, and a very small gap 7 is formed sandwiched between thesubstrate and polysilicon film 6. Then as shown in FIG. 10, the siliconoxide film 9 is formed according to the CVD method to cover thesubstrate and polysilicon film 6, and is processed into a desired formby the photo etching technique. Since the gap is formed almost undervacuum, it serves as a pressure reference chamber when it isvacuum-sealed and used as an absolute pressure sensor. After that,polysilicon film 10 is formed on the oxide film 9 as surface protectivefilm by the CVD method, as shown in FIG. 11, and is processed into adesired form by the photo etching technique. It is preferred cover thesealed oxide film 9 entirely with the polysilicon film 10 from themoisture-proof surface, as shown in FIG. 11. However, there is no needof covering it entirely as shown in FIG. 12, if the distance from theend of the polysilicon film 10 to the etch channel 12 is sufficientlylong, based on the relationship between the thickness of the siliconoxide film and permeation of water shown in FIG. 3, when considerationis given to the service life and permeation speed of moisture in theoxide film. In the present embodiment, the distance from the end of thepolysilicon film 10 to the etch channel 12 is set to 10 microns. This isintended to ensure a durability of 10 years because the permeation speedof moisture is 1 microns per year according to our examination. Further,silicon nitride film can be considered as impermeable film, but siliconnitride film has a very large film stress of about 1.5 GPa. This willcause temporal deformation of the polysilicon diaphragm 6. To avoiddeformation, film thickness is set to 0.4 microns or less in thisembodiment. Further, to prevent pinholes from occurring, film thicknessis preferred to be 0.1 micros or more. Lastly, as shown in FIG. 13, acontact hole is opened by etching of silicon nitride film 5 and siliconoxide film 4, and photo etching is performed after sputtering ofaluminum. This process provides an aluminum lead 11 of fixed electrode 3and polysilicon movable electrode 6.

The structure discussed above is characterized in that a combination ofsilicon oxide film manufactured by the CVD method and polysilicon filmis used as a sealing material of etch channel. This simplifies thesealing structure and improves the resistance to moisture. Further,residual stresses of the oxide film and polysilicon film subsequent toformation of film are as small as about 0.15 GPa and 0.2 GPa,respectively. This reduces the temporal deformation of the diaphragm.

The following describes another embodiment according to the presentinvention. FIG. 14 is a cross sectional view representing one embodimentof a semiconductor pressure sensor according to the present invention.In this structure, a hole is created on the top surface of the diaphragm6. This hole is used as an etch channel 12, and a sacrificial layer isremoved to create a pressure reference chamber. Polysilicon and siliconoxide film can be considered as a sealing material for the etch channel12. In the case of polysilicon, the polysilicon having passed throughthe hole by the time hole sealing is completed is deposited on the fixedelectrode to form a column, with the result that a desired gap structurecannot be obtained. To solve this problem, the present embodiment adoptssilicon oxide film 9 as a sealing material. When oxide film formed bythe CVD method is used, a short time is required for sealing because ofa great amount of deposit on the side face of the hole, resulting in areduced amount of deposit on the fixed electrode. As described above,however, if oxide film alone is used for sealing, moisture may permeateoxide film in the environment of high humidity to enter the gap, and maycause changes in characteristics. To solve this problem, the wholesurface on oxide film is covered with polysilicon 10, similarly to theabove-mentioned embodiment, or part of the oxide film is covered toensure that the distance between the above-mentioned etch channel 9 andpolysilicon 10 exceeds a certain value, with consideration given toservice life and permeation speed of moisture in silicon oxide film, asshown in FIG. 15.

With reference to FIG. 16, the following describes the embodiment of thecircuit integrated type pressure sensor where a signal processingcircuit is integrated onto the pressure sensor according to the presentinvention. The pressure gage is manufactured according to the ICproduction process. This makes it easy to manufacture acapacitance/voltage conversion circuit consisting of the CMOS on thesame substrate. This sensor comprises a capacitor 21 for pressuredetection, capacitor 22 for reference, oscillator 23, capacitancedetecting circuit 24, computing circuit 25 for output adjustment,amplifier 26 and electrode pad 27. FIG. 17 illustrates the structure ofthe capacitor 22 for reference. The structure of the capacitor 22 forreference is almost the same as that of the capacitor 23 for pressuredetection. However, a columnar substrate fixed portion 31 is arrangedwithin the range of the diaphragm, and the diaphragm is fragmented. Thecapacitance is about the same as that of the capacitor for pressuredetection, and capacitance value is hardly changed by pressure. So itserves as a reference capacitance in the process of detecting thecapacitance to be discussed later. A MOS capacitor generally used as acircuit constituting component can be used as this capacitor 22 forreference. In the present embodiment, down sizing and cost cutting ofthe pressure sensor are achieved by integration of a pressure gage anddetecting circuit. Further, a substantial improvement of measurementaccuracy in capacitance detection can be realized due to reduced wiringcapacitance between the capacitor and circuit.

FIG. 18 illustrates a capacitance detecting circuit based on theprinciple of switched capacitance. The capacitor for pressure detectionand capacitor for reference (capacitance values are assumed as Cs andCr, respectively) are each connected with selector switches, and thestates of timing 1 and timing 2 alternate. In the state of timing 1, thecapacitor for reference and capacitor for pressure detection each arevoltage sources, and the electric charge in conformity to capacitancevalue is stored. In the state of timing 2, both of them are connected tothe input of the operational amplifier on the negative side. Electricalcharges stored in the capacitor for reference and capacitor for pressuredetection cancel each other, and the differential electrical chargeflows into the operational amplifier. The electrical charge flowing intothe operational amplifier charges the integral capacitor Cf to changethe output voltage. Then when the state is shifted back to the state oftiming 1, output voltage is connected to the capacitor for pressuredetection to form a feedback loop. Since a negative feedback loop isformed, the amount of electrical charge in the capacitor for pressuredetection comes closer to that in the capacitor for reference every timetiming 1 and timing 2 are switched. They are kept in balance in thefinal stage, with the result that stable output voltage is ensured.Output voltage Vout at this time can be expressed as follows if thereference voltage is Vb:Vout=(1−Cr/Cs)*Vb

1/Cs exhibits almost a linear decrease with respect to applied pressure.So Vout shows almost a linear increase with respect to applied pressure.

FIG. 19 illustrates a the pressure sensor manufactured according to thepresent invention used as an intake pressure sensor of car enginecontrol system: After passing through an air cleaner 41, outside air isled into the intake tube 42, and flow rate is adjusted by a throttlevalve 43. Then the air is led into an intake manifold 44. A pressuresensor 45 according to the present invention is installed in the intakemanifold to detect the pressure inside the intake manifold 4. Based onthe signals of this pressure sensor 45 and engine speed, an enginecontroller unit 49 calculates the amount of intake. It calculates theamount of fuel to be injected best suited to the amount of intake, andthe calculated amount of fuel is sent to the injector 46. Gasolineinjected from the injector 46 is mixed with intake air to become gasmixture. It is fed into the combustion chamber when the intake valve 48opens, and is compressed by a piston 50. Then it is exploded and burntby a spark plug 47.

When the pressure sensor is used for a car engine control system as inthe present embodiment, the hermetic structure of the pressure referencechamber is required to be very strong when consideration is given to thefact that the engine room where the pressure sensor is installed has ahigh temperature, the sensor is used in the highly humid environment asin the rain and the service life of the car is as long as about tenyears. The air-tight sealed structure according to the present inventionis excellent in resistance to humidity, and sufficiently meets the aboveconditions.

The following describes an example where a very small gap structureproduced based on the present invention is applied to a piezoresistivepressure sensor. FIG. 20 illustrates a cross sectional view and FIG. 21shows a plan view. When phosphorus or other impurities are dispersed onthe top surface of the polysilicon 6, a strain gage 51 is formed on theperiphery of the diaphragm in a bridge shape. When voltage is applied tothe bridge circuit and pressure is applied to the diaphragm 6, thediaphragm is bent and a change occurs to the resistance of the straingage. A differential voltage occurs according to the pressure betweentwo output terminals of the bridge. The pressure can be measured byamplifying and reading this differential voltage. When this sensor isused as an absolute pressure sensor, a very small gap structure must bevacuum-sealed. A sensor excellent in durability can be provided by thesealed structure formed by a combination of silicon oxide film 9 formedby the above-mentioned CVD method and polysilicon film 10.

The following describes the case where a very small gap structureproduced according to the present invention is applied to thecapacitance type acceleration sensor: FIG. 22 is a cross sectional viewof the acceleration sensor where an overhang type beam 52 foracceleration detection is installed inside a vacuum-sealed very smallgap. The overhang type beam is a movable electrode. If the overhang typebeam is deformed by acceleration, there is a change in the gap with thefixed electrode installed on the substrate in a face-to-face position.This permits the acceleration to be detected as a change in capacitance.To increase the response, the interior of the gap must be vacuum-sealed.A sealed structure formed by a combination of the silicon oxide film 9according to the CVD method and polysilicon film 10 is effective.

Additionally, the sealing structure of the etch channel according to thepresent invention finds application in a semiconductor vibration gyrohaving a vacuum sealed cavity, rotating gyro and infrared sensor.

The following describes the packaging of the pressure sensor accordingto the present invention with reference to FIGS. 23 and 24. There arefollowing types to get the specified pressure value; a chip (gage chip)type sensor consisting of the capacitor for pressure detection andcapacitance detecting circuit as described above, a 2-chip type sensorcombined with a circuit chip to correct the output value, and a 1-chiptype sensor with a correction circuit built in the gage chip. Thefollowing description takes up the example of a 2-chip type sensor: Thegage chip 100 and circuit chip 101 is bonded on the lead framecomprising conductive metal formed on the resin-made sub-package 102using the adhesive; further, each electrode pad 125 on the chip and eachlead frame 105 are electrically connected by wire bonding. The circuitchip 101 can be sealed by the cover 120 to be discussed later. For themeasurement of atmospheric pressure, the gage chip 100 must be exposedto the atmosphere through the pressure intake tube to be describedlater. Depending on the environment for use, dust particle, gasoline andacid may be contained in the atmosphere. When the gage chip is exposeddirectly to the atmosphere, the chip may be damaged. To protect the chipagainst them, silicone gel 104 is applied on the surface of the gagechip 100. The sub-package 110 with the two chips bonded with each otheris further bonded to the resin-made housing 115 having a connector 111using adhesive and others. The connector 111 and circuit chip areelectrically connected by aluminum wire 112. In the final stage, a cover120 with resin-made pressure intake tube 113 is bonded to seal thecircuit, and this process is now complete. Adjustment is made in thefollowing steps: Firstly, pressure application test is conducted tomeasure the output voltage of the gage chip. Then corrections inconformity to the characteristics are stored in the ROM installed insidethe circuit chip 101. The above steps allows the sensor output to beadjusted to the specified output voltage. In the above case, asub-package is used in the present embodiment, but need not always beused. Furthermore, the 1-chip type sensor allows the packaging costs tobe cut down; for example, it permits the number of terminals to bereduced. The output of the circuit chip is output to the external signalline through the connector.

The present embodiment uses a combination of the oxide film manufacturedby the CVD method

-   -   and polysilicon film as an etch channel sealing material in a        pressure sensor manufactured by the sacrificial layer etching        technique. This allows an etch channel sealed structure to be        simplified, and prevents entry of moisture into the cavity,        thereby improving moisture resistance. Moreover, sealing        material with small film stress reduces temporal deformation of        the diaphragm.

1. A semiconductor pressure sensor, comprising: a substrate; a diaphragmarranged on said substrate, the diaphragm comprising an etch channel; asilicon oxide film covering said diaphragm and sealing said etchchannel; and a polysilicon film with a first side covering part or allof said silicon oxide film and a second side exposed to an environmentof the pressure sensor.
 2. A semiconductor pressure sensor according toclaim 1, wherein a distance of said covered part is at least 10 micronsor less from said etch channel.
 3. A semiconductor pressure sensoraccording to claim 1, wherein a thickness of said polysilicon film is0.1 microns or more.
 4. A semiconductor pressure sensor according toclaim 1, wherein a thickness of said polysilicon film is 0.1 microns ormore up to and including 0.4 microns.
 5. A pressure detector,comprising: (a) a detector providing an output, the detector includingas an integral unit; a substrate, a diaphragm arranged on saidsubstrate, the diaphragm comprising an etch channel; a silicon oxidefilm covering said diaphragm and sealing said etch channel, and apolysilicon film with a first side covering part or all of said siliconoxide film and a second side exposed to an environment of the pressuresensor; (b) a correction circuit for correction of the output of saiddetector; (c) a package enclosing said correction circuit and saiddetector; and (d) an intake tube provided in said package, the intaketube being used for introducing external pressure to said detector.
 6. Apressure detector according to claim 5, wherein a distance (h) of saidcovering part is at least 10 microns or less from said etch channel. 7.A pressure detector according to claim 5, wherein a thickness (i) ofsaid polysilicon film is 0.1 microns or more.
 8. A pressure detectoraccording to claim 5, wherein a thickness (j) of said polysilicon filmis 0.1 microns or more up to and including 0.4 microns.
 9. A pressuredetector according to claim 5 comprising: (e) a sub-package furthercomprising said correction circuit and said detector as an integralunit, and having on a surface a pad connected to said correctioncircuit; and (f) an output terminal removably connected to an externalsignal line and being used to send a signal from said correction circuitto the external signal line; wherein said correction circuit and saiddetector are enclosed by said package after said pad and said outputterminal are connected by a metal wire.
 10. A semiconductor pressuresensor, comprising: a substrate; a diaphragm arranged on the substrate,a gap between the diaphragm and the substrate being formed bysacrificial layer etching using etch channels arranged about a peripheryof the diaphragm; a silicon oxide film arranged over the diaphragm inorder to seal the etch channels; and a polysilicon film covering atleast a substantial portion of the silicon oxide film.
 11. Asemiconductor pressure sensor according to claim 10, wherein thepolysilicon film has a first side covering at least a substantialportion of the oxide film and a second side exposed to an environment ofthe pressure sensor.
 12. A semiconductor pressure sensor according toclaim 11, wherein the pressure sensor is an electrostatic capacity orpiezoresistive pressure sensor.